This invention relates in general to switching systems and more specifically to switching systems particularly suited for electronic channel selection in communication equipment.
In the evolution of two-way communication equipment, there is a demand to increase the number of channels on which the equipment can selectively operate. For mobile or portable radio equipment, it is also desirable to locate user operated controls, such as a channel selector switch, in a relatively small control head located at some convenient point of access to the user while installing the more bulky radio circuits at a less accessible location such as the trunk of a vehicle. Conventional mechanical switches have a common "pole" and a "throw" for each selectable channel. As the number of channels to be user selected grows with each generation of radio equipment, the size of conventional switches becomes large due to the high number of "throw" contacts required. Such switches, because of their bulk and high number of contacts, become inconvenient to use and impractical to fabricate.
Various alternatives to conventional switches have been attempted. Such alternatives include the use of push-button panel switches, and light beams for detecting switch movements. However, these approaches have not produced the highly desirable small size desired for a switch to be located in a control head. Another approach utilizes two separate and distinct switches in digital circuit. One such switch controls a "tens" place and the other controls the "units" place. In such systems, conventional switching techniques are used. Although the dual switch digital system achieves the small size objective, it is not convenient for the user to operate.
One known electronic channel selector scheme is shown in U.S. Pat. No. 4,065,720--Pogue, Jr. (1977). That particular arrangement utilizes a multiple position continuous rotation rotary switch having three states that are repeated cyclically. The switch has N discrete angular positions, N/3 movable angularly spaced grounded contacts and three stationary contacts positioned with predetermined angular spacing. As the movable contacts are rotated in a "clockwise" direction, the three stationary contacts are engaged and grounded in a first sequence by a movable contact. But, as the movable contacts are rotated in a counter-clockwise direction, the three stationary contacts are engaged and grounded in a second sequence, opposite to the first sequence. The stationary contacts are coupled to a three-state latch which provides a digital signal identifying the last of the stationary contacts to be grounded by a movable contact. The digital signal output of the three-stage latch is coupled to a flip-flop memory and to a switch position comparator and clock. The flip-flop memorizes the output of the three-state latch and provides, at an output thereof, a signal indicating the output of the three-state latch. The switch position comparator and clock compare the present position of the rotary switch, as represented by the output of the three-state latch, with the position of the rotary switch as represented by the output of the flip-flop memory. When the digital signal output of the three-state latch varies from the digital signal output of the flip-flop memory, up/down control signals are provided on output lines of the switch position comparator and clock to operate an up/down counter. The counter signals in turn effect channel selection.
Although the Pogue, Jr. system is effective for its purposes, it depends for its operation, upon a rather complex circuit arrangement. Also, the switch itself causes some operational disadvantage. It is not clear from the Pogue, Jr. specification whether his switch is provided with detents defining, in conjunction with the movable contacts, discrete angular positions of the switch. If detents are provided, it would take three (3) "clicks" to obtain one (1) count. This could, under certain circumstances cause a partially effective count. It is therefore desirable to further simplify the electronic switching arrangement to provide a more compact and easier to utilize operational control for radio equipment and one that can be manufactured in quantity more inexpensively than known switching arrangements.